High quality performance required in nuclear power plant systems is difficult to demonstrate when digital computers are involved. Special design considerations are needed to assure high quality performance of the digital computer program within the framework of the total system. Two ideas, discussed in this paper, contribute towards meeting the special considerations needed to incorporate software into a total system design in a highly safety-oriented industry. An orderly development process incorporates the software design into the early stages of the total system design. A graphic technique, SADTÂ¿ is presented as a means to plan, implement, and document the orderly development process. The use of digital computers increase the complex-ities of systems design. Contributions are made by diverse, highly specialized groups. The quality of system performance depends on the performance of each group and how well the individual contributions mesh together to form a total system. The system designer, the hardware designer, the software designer, and numerous others must coordinate their efforts to ultimately achieve an operational system which possesses evidence of high quality performance. To provide assurance that the digital computer program performs its intended function is a difficult task.